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<head><meta charset="utf-8"><title>regression due to rollup · t-compiler/performance · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/index.html">t-compiler/performance</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html">regression due to rollup</a></h3>

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<a name="204302995"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204302995" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> matthiaskrgr <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204302995">(Jul 18 2020 at 14:40)</a>:</h4>
<p>Looks like something in a recent rollup regressed a number of benchmarks <a href="https://perf.rust-lang.org/compare.html?start=39d5a61f2e4e237123837f5162cc275c2fd7e625&amp;end=d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02&amp;stat=instructions:u">https://perf.rust-lang.org/compare.html?start=39d5a61f2e4e237123837f5162cc275c2fd7e625&amp;end=d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02&amp;stat=instructions:u</a></p>



<a name="204303074"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303074" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> matthiaskrgr <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303074">(Jul 18 2020 at 14:42)</a>:</h4>
<p>PR: <a href="https://github.com/rust-lang/rust/commit/d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02">https://github.com/rust-lang/rust/commit/d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02</a></p>



<a name="204303102"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303102" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> matthiaskrgr <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303102">(Jul 18 2020 at 14:43)</a>:</h4>
<p><a href="https://github.com/rust-lang/rust/pull/74169">https://github.com/rust-lang/rust/pull/74169</a><br>
and<br>
<a href="https://github.com/rust-lang/rust/pull/74411">https://github.com/rust-lang/rust/pull/74411</a><br>
look suspicious to me but I'm a noob so take it with a bag of salt :P</p>



<a name="204303163"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303163" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303163">(Jul 18 2020 at 14:45)</a>:</h4>
<p>oh shit <span aria-label="sweat smile" class="emoji emoji-1f605" role="img" title="sweat smile">:sweat_smile:</span></p>



<a name="204303235"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303235" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303235">(Jul 18 2020 at 14:47)</a>:</h4>
<p>Crossing out the ones that couldn't have caused it:</p>
<ul>
<li><a href="https://github.com/rust-lang/rust/issues/71670">#71670</a> <del>(Enforce even more the code blocks attributes check through rustdoc)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/73930">#73930</a> <del>(Make some Option methods const)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74009">#74009</a> <del>(Fix MinGW <code>run-make-fulldeps</code> tests)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74056">#74056</a> (Add Arguments::as_str().)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74169">#74169</a> (Stop processing unreachable blocks when solving dataflow)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74251">#74251</a> <del>(Teach bootstrap about target files vs target triples)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74288">#74288</a> <del>(Fix src/test/run-make/static-pie/test-aslr.rs)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74300">#74300</a> <del>(Use intra-doc links in core::iter module)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74364">#74364</a> <del>(add lazy normalization regression tests)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74368">#74368</a> <del>(Add CSS tidy check)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74394">#74394</a> <del>(Remove leftover from emscripten fastcomp support)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74411">#74411</a> (Don't assign <code>()</code> to <code>!</code> MIR locals)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74416">#74416</a> (Use an UTF-8 locale for the linker.)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74424">#74424</a> (Move hir::Place to librustc_middle/hir)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74428">#74428</a> <del>(docs: better demonstrate that None values are skipped as many times a…)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74438">#74438</a> (warn about uninitialized multi-variant enums)</li>
<li><a href="https://github.com/rust-lang/rust/issues/74440">#74440</a> <del>(Fix Arc::as_ptr docs)</del></li>
<li><a href="https://github.com/rust-lang/rust/issues/74452">#74452</a> <del>(intra-doc links: resolve modules in the type namespace)</del></li>
</ul>



<a name="204303601"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303601" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> mati865 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303601">(Jul 18 2020 at 14:57)</a>:</h4>
<p><code>run_linker</code> is where this regression is coming from. <a href="https://github.com/rust-lang/rust/issues/74416">#74416</a> sounds unlikely but it's the only thing that modified linker code <span aria-label="shrug" class="emoji emoji-1f937" role="img" title="shrug">:shrug:</span></p>



<a name="204303650"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303650" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303650">(Jul 18 2020 at 14:58)</a>:</h4>
<p>Oh wow, it's not even marked red here <a href="https://perf.rust-lang.org/detailed-query.html?commit=d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02&amp;base_commit=39d5a61f2e4e237123837f5162cc275c2fd7e625&amp;benchmark=helloworld-opt&amp;run_name=full">https://perf.rust-lang.org/detailed-query.html?commit=d3df8512d2c2afc6d2e7d8b5b951dd7f2ad77b02&amp;base_commit=39d5a61f2e4e237123837f5162cc275c2fd7e625&amp;benchmark=helloworld-opt&amp;run_name=full</a></p>



<a name="204303664"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303664" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303664">(Jul 18 2020 at 14:59)</a>:</h4>
<p>I'll revert it</p>



<a name="204303716"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303716" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303716">(Jul 18 2020 at 15:00)</a>:</h4>
<p><a href="https://github.com/rust-lang/rust/issues/74478">#74478</a></p>



<a name="204303720"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204303720" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> mati865 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204303720">(Jul 18 2020 at 15:00)</a>:</h4>
<p>I was just about to create revert PR for perf but I don't mind.</p>



<a name="204305011"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204305011" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> bjorn3 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204305011">(Jul 18 2020 at 15:36)</a>:</h4>
<p>It could be that the UTF-8 handling in the linker is slow. It won't be the first program. For example <code>grep -i</code> is &gt;50x slower when handling UTF-8.</p>



<a name="204306099"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204306099" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> mati865 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204306099">(Jul 18 2020 at 16:04)</a>:</h4>
<p>I'm not going to look into BFD code (hopefully ever) again but maybe somebody else wants to check it?</p>



<a name="204324777"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204324777" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204324777">(Jul 19 2020 at 00:43)</a>:</h4>
<p>thankfully it's a small one</p>



<a name="204324787"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204324787" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204324787">(Jul 19 2020 at 00:43)</a>:</h4>
<p>how is BFD still in use :(. gold should be the legacy linker now with lld trying to reach feature parity</p>



<a name="204325345"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204325345" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Joshua Nelson <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204325345">(Jul 19 2020 at 01:02)</a>:</h4>
<p><span class="user-mention" data-user-id="119009">@eddyb</span> look, rust still supports centos 5 lol</p>



<a name="204325366"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204325366" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204325366">(Jul 19 2020 at 01:03)</a>:</h4>
<p>yeah but perf doesn't run on centos 5 does it?</p>



<a name="204332240"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332240" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> cuviper <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332240">(Jul 19 2020 at 04:21)</a>:</h4>
<p>re: centos 5, <a href="https://github.com/rust-lang/rust/issues/74163">#74163</a> will raise it a little</p>



<a name="204332282"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332282" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> cuviper <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332282">(Jul 19 2020 at 04:22)</a>:</h4>
<p>I tried centos 6, but a SUSE person still needs glibc 2.11, so we settled on a debian 6 builder</p>



<a name="204332284"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332284" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332284">(Jul 19 2020 at 04:22)</a>:</h4>
<p><span class="user-mention" data-user-id="138448">@cuviper</span> ooooh will this reduce our need to build two C++ compilers?</p>



<a name="204332294"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332294" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332294">(Jul 19 2020 at 04:23)</a>:</h4>
<p>looks like the PR doesn't remove the GCC+Clang combo :(</p>



<a name="204332578"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332578" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> cuviper <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332578">(Jul 19 2020 at 04:33)</a>:</h4>
<p>no, sadly the system gcc is still too old for llvm</p>



<a name="204332591"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332591" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> cuviper <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332591">(Jul 19 2020 at 04:33)</a>:</h4>
<p>we could maybe stagger it -- choose an older clang/llvm that does build with that system gcc, then use that in building rustc and its new llvm</p>



<a name="204332633"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332633" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> cuviper <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332633">(Jul 19 2020 at 04:34)</a>:</h4>
<p>anyway, the double compilers are cached in docker, so meh</p>



<a name="204332762"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332762" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332762">(Jul 19 2020 at 04:39)</a>:</h4>
<p><span class="user-mention" data-user-id="138448">@cuviper</span> that or maybe a GCC newer than 5 that still builds with the system LLVM? since GCC moves slower I think?</p>



<a name="204332803"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204332803" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204332803">(Jul 19 2020 at 04:40)</a>:</h4>
<p>yeah it should be fine once we switch to GHA, I just have recently seen rollups fail due to timeouts after rebuilding GCC on Azure :P</p>



<a name="204337822"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204337822" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> mati865 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204337822">(Jul 19 2020 at 07:47)</a>:</h4>
<p><span class="user-mention silent" data-user-id="119009">eddyb</span> <a href="#narrow/stream/247081-t-compiler.2Fperformance/topic/regression.20due.20to.20rollup/near/204325366">said</a>:</p>
<blockquote>
<p>yeah but perf doesn't run on centos 5 does it?</p>
</blockquote>
<p>It was using Ubuntu 18.04 before the migration to the new server, I don't know it this has changed.</p>



<a name="204338271"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204338271" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> mati865 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204338271">(Jul 19 2020 at 08:00)</a>:</h4>
<p><span class="user-mention silent" data-user-id="138448">cuviper</span> <a href="#narrow/stream/247081-t-compiler.2Fperformance/topic/regression.20due.20to.20rollup/near/204332591">said</a>:</p>
<blockquote>
<p>we could maybe stagger it -- choose an older clang/llvm that does build with that system gcc, then use that in building rustc and its new llvm</p>
</blockquote>
<p>Starting with LLVM 3.5 released 5 years ago I think require GCC &gt;= 4.7.0 and ThinLTO used on CI was included starting with LLVM 3.9 but was very buggy back then. I don't think it's possible to keep ThinLTO with older LLVM and if we don't do ThinLTO we can avoid building LLVM at all.</p>



<a name="204339968"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204339968" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204339968">(Jul 19 2020 at 09:00)</a>:</h4>
<p>what about newer GCC that can be compiled with system GCC, and which can compile current LLVM?</p>



<a name="204340014"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204340014" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204340014">(Jul 19 2020 at 09:00)</a>:</h4>
<p>to avoid what we do now which is:<br>
system GCC -&gt; build GCC 5 -&gt; use GCC 5 to build clang -&gt; use clang to build LLVM</p>



<a name="204340352"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204340352" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> andjo403 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204340352">(Jul 19 2020 at 09:11)</a>:</h4>
<p>to compile current llvm you need GCC 5.1 according to <a href="https://github.com/rust-lang/llvm-project/blob/86b120e6f302d39cd6973b6391fb299d7bc22122/llvm/cmake/modules/CheckCompilerVersion.cmake#L7">CheckCompilerVersion.cmake</a></p>



<a name="204340855"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204340855" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204340855">(Jul 19 2020 at 09:25)</a>:</h4>
<p>then why do we build clang?</p>



<a name="204340926"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204340926" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> andjo403 <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204340926">(Jul 19 2020 at 09:27)</a>:</h4>
<p>I think clang is built to be able to use thinLto when compiling llvm</p>



<a name="204341858"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204341858" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204341858">(Jul 19 2020 at 09:54)</a>:</h4>
<p>ohhhh we ThinLTO LLVM itself, not just enable the ThinLTO functionality in LLVM</p>



<a name="204341863"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/247081-t-compiler/performance/topic/regression%20due%20to%20rollup/near/204341863" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> eddyb <a href="https://rust-lang.github.io/zulip_archive/stream/247081-t-compiler/performance/topic/regression.20due.20to.20rollup.html#204341863">(Jul 19 2020 at 09:54)</a>:</h4>
<p>that wasn't clear at all in the Dockerfile I don't think <span aria-label="sweat smile" class="emoji emoji-1f605" role="img" title="sweat smile">:sweat_smile:</span></p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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